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Unlocked GSM Phone on CDMA

Hi, I have a T-Mobile Samsung Galaxy T GSM phone that is unlocked. Can I use this phone on the Verizon CDMA network? I always thought a quad band phone coudl be used on any network...isn't CDMA on 2 of the frequencies and GSM onthe other 2 frequencies? If so, couldn't the unlocked phone be used on any carrier if I get the correct sim card in it, meaning a CDMA sim card vs the GSM sim card I have now? Can someone explain this to me? I hate T-Mobile after just 9 months and I am going back to Verizon. But, we still owe $240 on the two Gravity T's we own, and hate to just throw $240 away by putting them in the drawer when we go back to Verizon and get new phones from Verizon. We would liek to use the Gravity T's on Verizon..they are unlocked!

There is no such thing as a CDMA SIM. CDMA is built into the phone. A quad band GSM phone is global, meaning if you travel outside of the United States, you can slip in a new SIM card use your phone there then switch back. The bad news is your phone works with GSM only but is unlocked for any GSM carrier. You will need to get a Verizon branded phone for use on Verizon's network.

Ok, thanks for explaining it to me. Unlocked for GSM networks anywhere in the world only. And, from what I found last night on this forum after posting my question is that a dual-mode, quad band phone will work on both the CDMA and GSM networks. Shoot...I hate throwing away a phone but I hate T-Mobile's coverage and customer service. Ugh...

Ok, thanks for explaining it to me. Unlocked for GSM networks anywhere in the world only. And, from what I found last night on this forum after posting my question is that a dual-mode, quad band phone will work on both the CDMA and GSM networks. Shoot...I hate throwing away a phone but I hate T-Mobile's coverage and customer service. Ugh...

Even if your phone was CDMA capable, you still wouldn't be able to activate it on a new line of service with Verizon because it's not a Verizon branded phone. The GSM side of the phone is easy to unlock with a simple code provided by your carrier. CDMA is more complex because the phone is flashed with software making it carrier specific. For instance, even if you went into a Verizon store with a Sprint phone which is the same CDMA technology, they wouldn't activate it for you. The first reason being your ESN would not be in Verizon's database since it isn't their phone. The beauty of GSM is once a phone is unlocked, you can now get a SIM from the GSM carrier of your choice and keep your same phone. Around here, CDMA has far superior coverage, but is more of a racket because they make you get a whole new phone to change carriers. Verizon makes money by signing new contracts so the first thing you will be told is you need to buy one of their phones. CDMA phones are not locked like GSM phones but they are carrier specific by their software and ESN number. So even if you had a phone that was capable roaming CDMA, it still couldn't be activated on Verizon.

Just in case you heard about a CDMA SIM, those are for LTE 4g data only and won't fit in a GSM phone. Something you may be reading about would be a CDMA world phone which uses a SIM for overseas GSM roaming. Keep in mind these phone operate on both CDMA and GSM but they are designed to run on CDMA as their home carrier and GSM roaming works overseas only.

A great & easy to understand explanation. Software...never would have guessed that would be a limiting factor..."they" always can find a way to control you....

EBay is an option but...if my unlocked GSM phone will work with a different country SIM card then perhaps we should just keep them for when we travel. Hmmm...something to think about...

I am now considering an older phone..a UTStarcom XV6700, a HTC XV6800, or one of two Samsung phones: a SCH-i730 or a SCH-i760..they are between $20 - $50, are wi-fi capable, and were "the" smartphones from a few years back..so they should be better quality and have better features than the non-smartphones of today..and I am hopeful Verizon will activate them (via their 800 #, not a local store) without a dataplan.

A more complete explanation is that CDMA is a completely different communications protocol than GSM. It's like expecting an AM radio to receive FM signals. Now, just as there are AM/FM radios, there are dual GSM/CDMA mobile phones. A GSM-only mobile phone can not communicate on a CDMA network, and vice versa; but a dual phone can communicate on both by switching its modes between GSM and CDMA.

It gets more complicated when we get into generations. At the risk of gross over-simplification:

CDMA and GSM are 2G. There is a "faster" data upgrade in CDMA called 1xRTT, and in GSM called EDGE.

The 3G successor to CDMA is called EV-DO.

The 3G successor to GSM is called by various names, including UMTS, HSPA, and very confusingly W-CDMA (there are differences between these forms; but for the most part you can ignore them). Let's use "UMTS" as shorthand for all of these. Some CDMA carriers chose to go with UMTS for 3G instead of (or in addition to) EV-DO.

In 4G, pretty much everybody is going to LTE. There is also something called WiMax which SPRINT uses; but the other CDMA providers did not choose it.

Depending upon how you look at it, either "GSM won" because LTE is ultimately a GSM successor; or "CDMA won" because all 3G and 4G systems are ultimately CDMA technology (GSM used TDMA technology, but is not compatible with the largely-historical TDMA networks of a decade or more ago).

Experts in this stuff will quickly say that what I've written above is far too simplistic (and I agree); but for most practical purposes this is good enough.

Something to consider, have you taken a look at Page Plus Cellular? I only bring this up because they are a Verizon MVNO that will allow you to activate Verizon branded smartphones without a data plan. Too extensive to explain here, but I have used a Palm Pixi Plus, far superior phone to the xv6800 and they've been as low as $36 shipped without a contract. I like the $30 monthly Page Plus plan with 1,200 voice minutes, 3,000 text and you do get 100mb data. For 2 phones it would still only be $60 monthly and each phone has it's own minutes/text/data. No M2M or free nights/weekends with Page Plus.

Of the phones you mentioned I like the XV6800 the best. I would strongly advise you go to the HTC website and download the WM update for the phone, if you download the correct update, your data should update to Rev.A. I did like the side out QWERTY keyboard for texting and having to dial a phone number manually was a bit of a pain, you almost need to use the stylus on the phone screen. I did like it better with a hard plastic cover, I found the side buttons weren't as easy to bump that way. Being WM it does sync with Outlook, so you can update contacts and calendar on your pc, which is something I liked. I'm not important enough to need email pushed to my phone, but it is a nice feature.

After you activate the phone, I suggest setting up a myverizon account online so you can verify they did not automatically add a data plan to your phone. I don't know if I was right or not, but I just changed the connection settings in my phone when I didn't want to connect to data. By selecting something like "use work network" nothing will happen if the browser is opened by accident. I'd have to say the phone is okay, but clearly not worth a $30 data plan. Might as well get a Droid Eris if you have to take a data plan, way better phone for about the same price.

Depending upon how you look at it, either "GSM won" because LTE is ultimately a GSM successor; or "CDMA won" because all 3G and 4G systems are ultimately CDMA technology (GSM used TDMA technology, but is not compatible with the largely-historical TDMA networks of a decade or more ago).

While all 3G system are based on CDMA technology, 4G systems most certainly are not. WiMax and LTE (as well as the now defunct UMB) are all based on OFDMA, which is completely different from CDMA.

I am a little confused. My Verizon phone was able to roam on GSM because they used TDMA. Tell it was shutdown. The phone recognizes it as Analog. If PCS has TDMA, It could be technically be used on GSM.

Originally Posted by Tabla

Y'know, I'm used to hysterical 14-year-old ******** on the internet, but this is exceptional. Never before in human history have so many nerds hyperventilated so publicly over so little.

but...if my unlocked GSM phone will work with a different country SIM card then perhaps we should just keep them for when we travel.

Thanks again for the explanation !

There is another small piece of the pie ... I'm quoting here from Phonescoop ... "GSM 850 is not compatible with GSM 900 used in Europe and Asia. A phone that only has GSM 850 cannot work on a GSM 900 network, nor vice-versa." I believe MOST of the new GSM phones include all bands, and THINK the "world phone" term ensures that. I'm unsure if all "world phone" equipment includes CDMA, but certainly all from Verizon would.

You all are fantastic. I love the explanations...they may be simple but they get the basics of the technology across to a layman...me, and if I need further detail, I know it exists and I can go find it.

While all 3G system are based on CDMA technology, 4G systems most certainly are not. WiMax and LTE (as well as the now defunct UMB) are all based on OFDMA, which is completely different from CDMA.

I know all this. I did say that my explanation was "gross over-simplification".

Of course OFDMA is not CDMA; but its architecture has quite a bit more in common with CDMA (and is impacted by the CDMA patents) than the TDMA architecture used with 2G GSM; and as "gross over-simplification" we can say that 4G ultimately comes from CDMA."

Nonetheless, you are correct; the evolutionary leap from 3G to 4G is quite a bit more than from 2G to 3G. The limitations of CDMA were reached, just as the limitations of TDMA were reached in the 2G->3G transition.

Of COURSE there is a CDMA SIM (CSIM). Heck, Verizon uses them now (the SIM card in LTE phones is USIM/CSIM combined). But to the OP, no, your phones don't support CDMA. Sorry.

"Just in case you heard about a CDMA SIM, those are for LTE 4g data only and won't fit in a GSM phone. "

Where did you get that idea? You denied they even existed then make this claim:

1. They are NOT for LTE 4G data only. They're CSIM/USIM combined cards.
2. Of course they'll FIT in a GSM phone. They're the same UICC 2nd form factor card. Heck, the GSM phone will even be able to read the USIM application and attempt to connect to a network. Of course it won't be allowed on any network that phone can see, but it'll FIT just fine.

For instance, even if you went into a Verizon store with a Sprint phone which is the same CDMA technology, they wouldn't activate it for you. The first reason being your ESN would not be in Verizon's database since it isn't their phone.

My personal experience has been quite different. I have never had a problem activating a Sprint branded phone on Verizon. Never had a problem with an AMP'D branded phone either.

Actually, the only phone I have ever had a problem with, was a Verizon branded SonyEricsson phone. Verizon claimed it was not e911 compatible. Of course, they were wrong. I offered to fax them a copy of the page from its Users Manual that states clearly it is e911 compatible, but Verizon didn't care a bit.